Microtubules are used by cells to maintain a non-spherical shape, serve as a supporting structure, to divide, and to secrete cellular components. They are influenced by a group of other proteins (microtubule associated proteins or MAPs) to control their assembly and disassembly. Unraveling the in vivo mechanism of this process is an important frontier in cell biology. The number, length, and orientation of microtubules (MTs) is regulated in the cell. Microtubule functions such as transport of organelles and secretion may also be regulated. We propose that changes in MT assembly and function in response to the cells changing physiological state may be mediated by Microtuble associated enzymes of which we have chosen the most promising prospects for study. We will characterize Nucleosidediphosphate kinase (NDPK) isolated from MT protein preparations. We will determine whether NDPK is associated with MTs in the cell and study the role of this enzyme in MT assembly, in vitro. We will determine whether NDPK is a transphosphorylase and study the role of transphosphorylation in assembly. We will characterize the MT associated protein kinase. We will explore two hypothesized functions for MT protein phosphorylation by determining whether MT phosphorylation regulates the rate of opposite end assembly - disassembly of MTs at steady state (treadmilling) and whether MT phosphorylation is involved in the binding of membrane bound vesicles to MTs. The regulation of MT protein kinase by polyamines, Ca2+, and calmodulin will be studied as will the effects of these three protein kinase regulators on treadmilling. We will study the role of phosphatidylinositol and phosphatidylinositol turnover by MT associated enzymes on the binding of lipoprotein secretory vesicles to microtubules. We will determine whether a defect in vesicle binding to MTs is responsible for the fatty liver induced by myo-inositol deficiency in the lactating rat.